Vegetation and soil feedbacks on the response of the African monsoon to orbital forcing in the early to middle Holocene
Vegetation and soil feedbacks on the response of the African monsoon to orbital forcing in the early to middle Holocene
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DOI：
10.1038/384623a0
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发表时间：
1996-12-19
期刊：
影响因子：
64.8
通讯作者：
Harrison, SP
中科院分区：
文献类型：
--
作者：
Kutzbach, J;Bonan, G;Harrison, SP
化石花粉、古代湖泊沉积物和来自非洲的考古证据表明，在全新世早期到中期，大约12，000到5，000年前，萨赫勒和撒哈拉地区比今天潮湿得多。与现代撒哈拉/萨赫勒边界有关的植被大约在北纬5度，在北纬15度到30度之间有更多更大的湖泊。气候模型的模拟表明，这些更潮湿的条件可能是由于地球轨道参数的变化造成的，这些参数增加了北方半球太阳辐射季节性周期的幅度，增强了陆地-海洋温度的对比，从而加强了非洲夏季季风（5-7）。然而，这些模拟低估了从古记录中推断的季风增强（4）。在这里，我们使用一个气候模型来表明，植被和土壤的变化可能增加了气候对轨道强迫的反应，我们发现，用全新世中期的轨道强迫取代今天的轨道强迫，在北纬15度到22度之间，夏季降水增加了12%。用草地代替沙漠，用更多的壤土代替沙漠土壤，进一步增加了夏季降水（分别增加了6%和10%），使总降水量增加了28%。当模拟的气候变化应用于生物群落模型时，在目前的撒哈拉/萨赫勒边界以北建立了植被，从而使撒哈拉的面积仅因轨道强迫而缩小了11%，由于轨道强迫和规定的植被和土壤变化的综合影响而缩小了20%，因此，纳入植被和土壤反馈，使模型模拟和古植被观测更接近一致。
FOSSIL pollen, ancient lake sediments and archaeological evidence from Africa indicate that the Sahel and Sahara regions were considerably wetter than today during the early to middle Holocene period, about 12,000 to 5,000 years ago(1-4). Vegetation associated with the modern Sahara/Sahel boundary was about 5 degrees farther north, and there were more and larger lakes between 15 and 30 degrees N. Simulations with climate models have shown that these wetter conditions were probably caused by changes in Earth's orbital parameters that increased the amplitude of the seasonal cycle of solar radiation in the Northern Hemisphere, enhanced the land-ocean temperature contrast, and thereby strengthened the African summer monsoon(5-7). However, these simulations underestimated the consequent monsoon enhancement as inferred from palaeorecords(4). Here,ve use a climate model to show that changes in vegetation and soil may have increased the climate response to orbital forcing, We find that replacing today's orbital forcing with that of the mid-Holocene increases summer precipitation by 12% between 15 and 22 degrees N. Replacing desert with grassland, and desert soil with more loamy soil, further enhances the summer precipitation (by 6 and 10% respectively), giving a total precipitation increase of 28%. When the simulated climate changes are applied to a biome model, vegetation becomes established north of the current Sahara/Sahel boundary, thereby shrinking the area of the Sahara by 11% owing to orbital forcing alone, and by 20% owing to the combined influence of orbital forcing and the prescribed vegetation and soil changes, The inclusion of the vegetation and soil feedbacks thus brings the model simulations and palaeovegetation observations into closer agreement.